This invention relates to a laminated aerostat material and an aerostat formed of such materials.
Aerostats are lighter-than-air inflatable balloons comprising a hull fabricated from sheet material and further including fins located at the tail of the hull for aerodynamic stability.
Aerostats are disclosed, for example, in U.S. Pat. Nos. 3,519,530 and 4,762,295, the entire disclosures of which are each incorporated by reference herein.
The sheet material used to form the hull of prior art aerostats has evolved to encompass a laminate material with or without strengthening filaments or metal foil layers. For example, the aforementioned U.S Pat. No. 3,519,530 discloses that two thermoplastic sheets can be pressed together under the influence of heat to embed strength filaments between them. Prior to or subsequent to this embedding operation, the thermoplastic sheets may be coated with an adhesive on their exterior sides and then laminated to sheets of non-thermoplastic material. Such non-thermoplastic material may comprise Mylar.RTM., or other similar plastic, or metal foil such as aluminum foil. Among suitable thermoplastic materials are disclosed polyethylene, polypropylene, polyvinyl materials, such as polyvinyl acetates and polyvinyl chlorides, nylon, etc.
Other prior art laminates are difficult to fabricate into the hull structure of aerostats. Difficulties in adhering the various plies of the laminate to one another, as well as to themselves, is not only difficult but significantly increases production costs but also makes it necessary to make all attachments to the aerostat hull through the fabric of the hull, rendering the construction prone to puncture and flex-cracking.
The aforementioned U.S. Pat. No. 4,762,295 discloses a laminate material comprising an outer coating of light-stable white pigmented polyester polyurethane applied onto a layer which is formed from 4.1 ounce/yard.sup.2 polyester woven fabric. The next inner layer is a coating of black pigmented polyester polyurethane with a further inner layer of non-woven oriented fiber polyester fabric. The innermost layer is a coating of a black pigmented polyether polyurethane. This material has a helium holding layer on only one side and its bias stability is poor.
Other prior art attempts to make hull structures with two-ply fabrics, generally with one ply biased at 45.degree. to provide dimensional stability (an example of which is The Goodyear Blimp). These structures are expensive due to the need for biasing, have a low strength/weight ratio, and frequently have ply separation problems.
Thus, there exists a long-standing need for a multi-layered laminate material which has particular utility for a gas-holding function as arises in the field of aerostats and which is free of the problems of the prior art materials.